1. Field of the Invention
The present invention relates to plasma processing apparatuses and, more particularly, to a plasma processing apparatus having a gas-introducing part, which introduces a reactant gas into a process chamber.
2. Description of the Related Art
In recent years, a plasma processing apparatus is used to perform a film deposition process, an etching process or an ashing process in a manufacturing process of semiconductor devices since the semiconductor devices have become more densified and a finer structure. For example, in a typical microwave plasma processing apparatus, a 2.45 GHz microwave is introduced into a process chamber through a slot electrode. An object to be processed such as a semiconductor wafer or an LCD substrate is placed inside the process chamber, which is maintained under a negative pressure environment by a vacuum pump. Additionally, a reactant gas is also introduced into the process chamber so that the process gas is converted into plasma by the microwave. Thus, active radicals and ions are generated, and the radicals and ions react with the object to be processed, which achieves a film deposition process or an etching process.
The reactant gas is introduced into the process chamber through gas supply nozzles provided on a sidewall of the process chamber. Alternatively, the reactant gas is introduced into the process chamber through a dielectric plate provided under a slot electrode, which is provided on a top of the process chamber. The gas supply arrangement including such a gas supply nozzle or a dielectric plate is subjected to an evacuating process by a vacuum pump, which is provided to evacuate gas inside the process chamber.
However, there is a problem in the conventional plasma processing apparatus in that residual impurities such as a water component cannot be completely removed from inside the process chamber. A water component adhering on the inner wall of the process chamber is evaporated due to a vacuum being formed in the process chamber, and the water vapor is released to the atmosphere inside the process chamber. The water vapor is exhausted out of the process chamber by a vacuum pump. However, since the gas-introducing part provided to the process chamber has gas-introducing holes (nozzles) each having a very small diameter, a removal speed of the water component remaining inside the gas-introducing part is low. Accordingly, some amount of water component tends to remain inside the gas-introducing part of the process chamber.
The water component remaining inside the gas-introducing part may enter and close the gas-introducing holes, which interrupts the introduction of the reactant gas into the process chamber. Thus, a yield rate of the object to be processed is deteriorated. Additionally, if some of the gas-introducing holes are closed, this may deteriorate a uniform distribution of the reactant gas in the process chamber, which may result in an uneven degree of processing of the object to be processed. Further, if the water component in the gas-introducing holes is ejected into the process chamber, the water component acts as an impurity, which deteriorates a high-quality process to be applied to the object to be processed.